Traditional surgical procedures are conducted by making an incision in the patient's body to expose those organs which are to be treated. The physician can observe the treatment directly and can guide tools such as surgical instruments to the site requiring treatment by direct visual observation. In typical endoscopic procedures, an elongated probe having a visual observation device such as a lens and fiber optic system or a small television camera is inserted into the patient's body and guided to the desired treatment location using observation of the visual image acquired by the visual observation device. The observation device can also be used to monitor additional probes such as tools inserted through the bore of a hollow endoscope or separate surgical instruments advanced through the same or other orifices to the treatment location. Endoscopic procedures suffer from various limitations. They require relatively bulky optical elements at the distal end of the endoscope. Moreover, the physician must conduct the procedure based on a limited picture delivered by the optical system.
Image-guided interventional procedures have been developed. In image-guided procedures, an imaging device such as an x-ray device is employed to monitor the position of a probe within the body. In the simplest image-guided procedures, a fluoroscope can be used to observe the position of a radioopaque probe while the probe is inserted into the body. Fluoroscopic and other x-ray imaging modalities have serious drawbacks, including exposure of the patient and physician to ionizing radiation and inability or limited ability to image soft tissues. Accordingly, treatment methods relying on x-ray based imaging for guidance of an intrabody probe have been applied only in limited circumstances.
Magnetic resonance imaging offers the unique ability to obtain excellent images of all tissues in a patient's body without the use of ionizing radiation. MRI typically requires the use of a large magnet to apply a strong magnetic field in a patient receiving space, large enough to accommodate that region of the patient's body which is to be imaged. Some early types of MRI imaging apparatus using superconducting magnets had a patient-receiving space essentially surrounded by components of the apparatus, making it impractical to perform interventional procedures while the patient is being imaged. However, some current MRI apparatus provides an "open" environment so that a patient disposed in the imaging space of the apparatus is accessible to physicians and other medical personnel. For example, magnetic resonance imaging apparatus of the type illustrated in U.S. Pat. No. 5,754,085 provides open access to the patient so that a patient positioned within the magnet is readily accessible to a physician standing outside of the magnet, making it practical to perform MRI-guided interventional procedures. In such procedures, MRI images may be continually acquired while a probe such as a catheter, endoscopic instrument, or other device is advanced into the patient. The MRI images desirably show internal structures of the patient's body and also depict the probe.
The MRI images allow the physician to visualize the disposition of the probe relative to the organs and tissues of the body and allow the physician to maneuver the probe along a desired trajectory within the body. For example, the physician can use MRI images to guide a probe within a tubular or cavernous organ such as within the circulatory tract, digestive tract, respiratory tract or urinary tract. Also, the physician can guide a probe within soft tissue as the probe is advanced through the soft tissue as, for example, through muscle, lung tissue or the like. The MRI images can also be used to monitor the progress of the treatment being performed. For example, if particular tissues such as tumors are being removed, the MRI images can show the tumor in contrast to the surrounding tissue and can show the physician where additional tissue must be removed.
Despite all this progress in the art, still further improvements in image-guided interventional procedures would be desirable.